123.sagews

x = var('x')
P = plot(13/2 + 1/2*x, -20, 20,rgbcolor=(1,0,0)) + \
    plot(2*x - 13, -15, 20,rgbcolor=(0,1,0))
P.show(ymin=-15,ymax=20, xmin=-15, xmax=20, figsize=[10,10])

x = var('x')
P = plot(13/2 + 1/2*x, -20, 20, rgbcolor=(1,0,0), linestyle='--') + \
    plot(2*x - 13,-15,20,rgbcolor=(0,1,0))                        + \
    plot(8 + 1/2*x,-20,20,rgbcolor=(0,0,1))                       + \
    arrow((5, 9), (5, 10.5), width=1, arrowsize=5, rgbcolor=(0,0,0))
P.show(ymin=-15,ymax=20, xmin=-15, xmax=20, figsize=[10,10])

x = var('x')
P = plot(13/2 + 1/2*x, -20, 20, rgbcolor=(1,0,0), linestyle='--')    + \
    plot(2*x - 13, -15, 20,rgbcolor=(0,1,0), linestyle='--')         + \
    plot(8 + 1/2*x, -20, 20,rgbcolor=(0,0,1))                        + \
    plot(2*x - 14, -15, 20, rgbcolor=(0,0,0))                        + \
    arrow((5, 9), (5, 10.5), width=1, arrowsize=5, rgbcolor=(0,0,0)) + \
    arrow((8.5, 5), (10, 5), width=1, arrowsize=5, rgbcolor=(0,0,0))
P.show(ymin=-15,ymax=20, xmin=-15, xmax=20, figsize=[10,10])